Power Cycling of Discrete SiC Power MOSFET Packages: Electro- Thermo-Mechanical Modeling of Bondwires

Abstract:
This paper presents an analysis of bond wire degradation under power cycling (PC) tests of discrete SiC power MOSFETs for a wide range of temperature swings (DT) using Finite-Element-Method-based electro-thermo-mechanical (ETM) modeling. Temperature-dependent material properties of epoxy mold compound (EMC) encapsulation and the elasto-plastic behavior of aluminum bond wires are taken into account. The plastic dissipation energy per cycle, Wp;END, related to the wire wear-out is simulated and its dependance on the PC parameters such as DT, the minimum junction temperature Tvj;min, and the heating time tON is evaluated in a wide range of DT. A direct correlation of Wp;END to the PC lifetime and the number of cycles-to-failure, Nf, allows estimating the Nf behavior at low DT, which is tedious to obtain experimentally. The results indicate that the plastic deformation of the bond wires significantly decreases at low DT, which affects not only Nf(DT) but also the Nf(tON) and Nf(Tjm) behavior from high to low DT regime. Furthermore, the impact of EMC properties on Wp;END is evaluated, clarifying the large differences between the PC capabilities of discrete SiC power MOSFETs from different manufacturers. The presented results are highly valuable for extrapolating the experimentally PC lifetime models towards low temperature swings, which are more relevant for actual mission profiles.